The present invention generally relates to an apparatus for detecting a transmission line, and more particularly, to an electronic apparatus for automatically detecting the length of a network transmission line.
With rapid developments of the electronics industry and computer technology, many electronic products are more and more widely used to improve quality of life. Particularly, many monitors for computer systems are utilized in the office and factory. In general, a color-added method is often used for color mixing to display colors on the monitor. In other words, the three primary colors, red, blue, and green generate a variety of images by superposition. In addition, the display intensity of the images is adjusted by controlling the voltage of output signals since monitors are analog modes normally so that all the pixels can be displayed in continuous color levels for a high quality display.
The video graphics array (VGA) is often used as the standard display specification. The VGA display mode can support the text mode and the graphic mode, which are compatible with most types of monitors used in computer systems. FIG. 1 shows a transmission mode of VGA video frequency in accordance with the prior art. In the computer system 100, a VGA video frequency signal is transmitted into the monitor 106 from video adapter 102 via network transmission line 104. However, the VGA video frequency signal decays due to the difference of impedance matching. If the VGA video frequency signal is under-balanced, the images are not clear when observed on the monitor 106. In contrast, if the VGA video frequency signal is over-balanced, over-excited signals are formed on the display, resulting in a reduction of monitor lifetime.
Specifically, various types of network transmission lines 104, such as a shielding twisted pair (STP) and a foil twisted pair (FTP), have distinct frequency responses. In the period of transmission, the VGA video frequency signal exhibits a severe decay phenomenon. When the length of network transmission line 106 is over ten meters, the video frequency signal is considerably lessened. This may degrade the quality of display images and even cause an operation error because of the unclear display.
Consequently, there is a need for an optimum video frequency to show clear display images so that the operation efficiency of the computer systems 100 is substantially increased while computer systems are transferring video frequency signal.
In view of the problems encountered with video frequency signal of the conventional monitor, conventional transmission is severely limited by the length of the transmission line. Video frequency cannot be transmitted to a remote monitor since the video frequency decays considerably.
As a result, the primary object of the present invention is to utilize an electronic apparatus for detecting a reference signal referred to generate a detection signal and to output a control signal via a microprocessor.
Another object of the present invention is to convert the video frequency signal into a differential signal which is incorporated into a control signal and outputted into a compensator device to make up for the differential signal and eventually form clear images on the monitor.
According to the above objects, the present invention sets forth the electronic apparatus for automatically detecting the length of a network transmission line. The electronic apparatus comprises a detection device, an analog/digital (A/D) converter, a microprocessor, a frequency compensator and a network transmission line, such as RJ-45 network line, connected to a remote computer server.
The detection device for generating the frequency response of a reference signal essentially comprises a transistor detector, a temperature compensation circuit, an emitting follower, a zero-adjusting circuit and a differential amplifier.
The transistor detector is used to detect a detection level of the reference signal. The zero-adjusting circuit can generate a zero level for reference. The differential amplifier amplifies the difference between the detection level and the zero level to generate a detection signal. Preferably, the differential amplifier includes a plurality of amplifiers and resistors.
The analog/digital (A/D) converter, coupled to the detection device, is able to convert the detection signal from the detection device into a digital signal to generate a full-scale level via a reference voltage. The microprocessor, coupled to the A/D converter, transfers digital signals into control signals to simultaneously control a plurality of switches for decaying the over-compensation portion of the video frequency.
The frequency compensator, coupled to the microprocessor via a network transmission line, comprises a frequency-gained circuit, a negative decayed device, a pull-up circuit, a positive decayed device and other amplified circuits. The frequency-gained device is used to adjust the bandwidth of the video frequency to the maximum level corresponding to the maximum length of the transmission line. The negative decayed device, coupled to the frequency-gained circuit, is able to decay the over-compensation portion of the video frequency for calibrating the video frequency. The pull-up circuit receives the video frequency and then increases the signal level of video frequency, such as the signal level between base and emitter (BE) of a transistor.
The positive decayed device, coupled to the pull-up circuit, is capable of decaying a positive over-compensation portion of the video frequency. Thereafter the negative over-compensation portion and the positive over-compensation portion of the video frequency are simultaneously output to a monitor by the differential amplifier. The positive decayed device preferably comprises a plurality of decayed circuits. Additionally, the electronic apparatus has connectors, such as RJ-45 and RJ-11 connectors, for receiving the transmission line in remote computer systems.
In summary, the electronic apparatus allows detection of the length of the transmission line and then generates a compensated video frequency signal which is output into the monitor such that the remote monitor can display a clear image for the benefits of operation convenience.